In recent years, with the reduction in size and weight for electronic devices, multilayer ceramic capacitors have been widely used which are small in size and capable of achieving high capacitance. This multilayer ceramic capacitor is, for example, as shown in FIG. 6, structured to have external electrodes 54 (54a, 54b) provided, so as to be electrically connected to a plurality of internal electrodes (52a, 52b), on a pair of mutually opposed end surfaces 53 (53a, 53b) of a multilayer ceramic element (ceramic laminated body) 60 obtained by laminating the internal electrodes 52 (52a, 52b) with ceramic layers 51 as dielectric layers interposed therebetween.
Further, in such a multilayer ceramic capacitor, a method of forming external electrodes by applying and baking a conductive paste including a conductive component such as a metal powder, a glass powder, and a vehicle is widely used as a method for forming the external electrodes.
As one of such methods, a method is proposed in which external electrode are formed on the surface of an electronic component element (multilayer ceramic element) or the like by firing at a firing temperature of 600 to 670° C. with the use of a conductive paste containing, in glass frit, B2O3: 9.0 to 20.0 weight %, SiO2: 22.0 to 32.0 weight %, BaO: 35.0 to 45.0 weight %, ZnO: 0.1 to 30.0 weight %, Al2O3: 0.1 to 12.0 weight %, Na2O: 0.1 to 15.0 weight % in terms of oxide (see Patent Document 1).
Further, when external electrodes are adapted to be formed by the method in Patent Document 1, defect generation caused by melting of internal electrodes (silver) provided in an electronic component element (multilayer ceramic element) is supposed to be allowed to be suppressed, and external electrodes which have adequate adhesive strength to adhere to the electronic component element are supposed to be able to be obtained (paragraph 0046 in Patent Document 1).
However, in the case of the conventional method, as described in an example thereof, firing in an air atmosphere is presupposed. For example, in the case of an electronic component with a non-precious metal of nickel (Ni) as internal electrodes and copper (Cu) as external electrodes, when firing in a neutral to reducing atmosphere is adapted to be applied because there is a need to prevent the electrodes form being oxidized, firing at a low temperature of, for example, 600 to 670° C. as disclosed in Patent Document 1 has the problem of insufficient degreasing, thereby resulting in failure to achieve densification of the external electrodes.
Alternatively, in the case of firing at high temperature, densification becomes possible, but there is a problem of eluting the internal electrodes into glass and interfering with contact with the external electrodes when glass contained in the external electrodes is not appropriate.
In contrast, when the internal electrodes are exposed adequately from the multilayer ceramic element in order to ensure the contact between the internal electrodes and the external electrodes, there is a problem that excessive interdiffusion between the metal constituting the external electrodes and the metal constituting the internal electrodes expands the internal electrodes to crack the ceramic constituting the multilayer ceramic element, thereby decreasing the mechanical strength and moisture resistance reliability.
Patent Document 1: Japanese Patent No. 3534684